The fabrication of semiconductor devices, such as light-emitting diodes (“LEDs”), typically involves an intricate manufacturing process with a myriad of steps. The conventional end-product of the fabrication is a “packaged” semiconductor device. The “packaged” modifier refers to the enclosure and protective features built into the final product as well as the interface that enables the device in the package to be incorporated into a circuit.
The conventional fabrication process for semiconductor devices starts with handling a semiconductor wafer. The wafer is diced into a multitude of “unpackaged” semiconductor devices. The “unpackaged” modifier refers to an unenclosed semiconductor device without packaging features. Herein, unpackaged semiconductor devices may be called semiconductor device dies, or just “dies” for simplicity. A single semiconductor wafer may be diced to create dies of various sizes, so as to form upwards of more than 100,000 or even 1,000,000 dies from the semiconductor wafer (depending on the starting size of the semiconductor), and each die has a certain quality. The unpackaged dies are then “packaged” via a conventional fabrication process discussed briefly below. The actions between the wafer handling and the packaging may be referred to as “die preparation.”
In some instances, the die preparation may include sorting the dies via a “pick and place process,” whereby diced dies are picked up individually and sorted into bins. The sorting may be based on the forward voltage capacity of the die, the average power of the die, and/or the wavelength of the die.
Typically, the packaging involves mounting a die into a plastic or ceramic package (e.g., mold or enclosure). The packaging also includes connecting the die contacts to pins/wires for interfacing/interconnecting with ultimate circuitry. The packaging of the semiconductor device is generally completed by sealing the die to protect it from the environment (e.g., dust).
A product manufacturer then places packaged dies in product circuitry. Due to the packaging, the dies are ready to be “plugged in” to the circuit assembly of the product being manufactured. Additionally, while the packaging of the dies protects them from elements that might degrade or destroy the dies, the packaged dies are inherently larger (e.g., in some cases, around 10 times the thickness and 10 times the area, resulting in 100 times the volume) than the unpackaged dies. Thus, the resulting assembly cannot be any thinner than the packaging of the semiconductor dies.
The thickness and overall size of the ultimate circuit assemblies including semiconductor devices has ramifications in multiple areas of technology. In the display industry for devices ranging from cell phones to televisions, for example, there is a drive to make the displays as thin as possible while simultaneously improving efficiency and quality of the displays. Some factors that continue to influence the thickness of the LED backlit LCD displays include: LEDs are relatively large, packaged LEDs; thick lenses that cover the LEDs between the optical substrates and the surface of the product substrate to which the LEDs are attached; inability to manufacture a thin LCD display using unpackaged dies in a cost-effective, qualitative, quantitative, uniform, and mass-reproducible manner; etc. For example, current industry techniques of LED backlighting for LCD displays include attaching (or possibly forming) a thick, preformed lens made of plastic, resin, or other materials over packaged LEDs on a circuit substrate. Such lenses may be as thick (tall) as 15 mm or more, and as wide (lateral diameter) as 35 mm or more. Further, the packaged LEDs are spaced significant distances apart to reduce heat and cost, including as much 40 mm and more between adjacent lenses of the attached LEDs. As such, the size (thickness) of the air gap between the backside of the optical substrates and the LEDs (and associated lenses) is significant, on the order of as much as 1-2 cm or more, in order to diffuse the emitted light sufficiently to minimize “hot spots” where the light shines brightly too close to the backside of the optical substrates and ends up creating a non-uniform brighter spot in the display device.